The present invention relates to a method of manufacturing a photomask and a photomask manufactured thereby, and more particularly, relates to a method of manufacturing a phase-shift (phase-shifting) photomask and a substrate etching-type phase-shift (phase-shifting) photomask manufactured thereby.
In these days, there has been remarkably developed an optical lithography technology for forming more fine resist pattern on a wafer. Such technology includes a phase-shift method, as one means for improving resolution of a projection/exposure device, in which phases of lights passing through two transparent portions adjacent to each other on a photomask are changed respectively.
This method is performed to carry out projection and exposure on the wafer by using a photomask formed so as to satisfy a relationship of d=xcex/2(nxe2x88x921) (in which d: film thickness; n: refraction factor; xcex: exposure wave length) as a shifter for inverting a phase on one of adjacent two light transmitting portions (in this meaning, the photomask may be called xe2x80x9cphase-shift photomask, hereinlaterxe2x80x9d), and the light passing the shifter has a phase reverse to that (180xc2x0 shift) of the transmitting light of the other on of the transmitting portions, so that light intensity at a pattern boundary portion becomes zero (0) and, thereby, the pattern is separated and the resolution is improved.
Examples of photomasks having shapes realizing the high resolution through the phase-shift method of the characters mentioned above are shown in FIG. 4.
FIG. 4A shows a shifter-formation type phase photomask in which a transparent medium 330, which may be called phase shift film or shifter, having a refraction factor different from that of air is provided for one of adjacent two openings 321 (light transmission sections) formed to a substrate 310. In such photomask, it is difficult to pile, with high performance, the phase-shift photomask having the same refraction factor as that of the substrate, and there is a possibility of occurrence of a further problem of multipath refraction at the phase shift film 330.
FIGS. 4B and 4C show other examples, to solve the above mentioned problem, of a phase shift photomask in which the transparent substrate is subjected to an etching working, which maybe called etching-type or etching-type phase-shift photomask.
With reference to FIG. 4B showing the example of etching type phase-shift photomask, an etched portion is formed through an aeolotropic etching process. In such photomask, an amount of light transmitting through the etched portion is reduced in comparison with that transmitting through a non-etched portion, and resist patterns of projection images corresponding to the etched portion and the non-etched portion have dimensions different from each other. This matter is known from the paper 1 (J.Vac.Sci.Technol. B 10(6) (1992) p.3055), R. L. Kostelak, [Exposure characteristics of alternate aperture phase-shifting photomasks fabricated using a subtractive process]).
Furthermore, with reference to FIG. 4C showing a phase-shift photomask, in which an etched portion is formed through an isotropic etching process. In such photomask, resist dimension difference is reduced in comparison with the photomask of FIG. 4B, which is also known from the above paper 1. This reduction is not, however, remarkable. The phase-shift photomask of FIG. 4C may be also called a single-etching type phase-shift photomask, and symbol Wa in FIG. 4C shows a side-etching amount (length).
Further, in the etching-type phase-shift photomask of FIG. 4B, the amount of light transmitting through the etched portion is reduced in comparison with the non-etched portion because of the existence of side walls of the etched portion, thus generating a difference in dimension to the corresponding resist patterns. Particularly, in the case of hole-arrangement-layer, the transmitting light intensities do not become equal and the dimension difference occurs in the resist patterns on the wafer. This phenomenon is remarkably observed for the hole pattern arranged obliquely less than 1.0 xcexcm.
Further, in general, the etching through the aeolotropic etching process is performed with dry-etching, and on the other hand, the isotropic etching is performed with wet-etching by using heat alkaline (sodium hydroxide) or hydrofluoric acid.
Furthermore, the prior art reference of the paper 2 (SPIE. Vol. 1927 (1933) p.28, Christophe Pierrat and others, [Phase-shifting Photomask Topography Effects on Lithographic Image Quality]) is known. In this paper 2, as a method of correcting or adjusting difference in dimension of a resist of the example shown in FIG. 4B, after etching vertically by an amount corresponding to 180xc2x0 phase difference through the aeolotropic etching process, which is a state shown in FIG. 4B, the isotropic etching process is effected to all the light transmitting section to thereby form an etching-type phase shift photomask represented by the example of FIG. 4D.
Further, the phase shift photomask shown in FIG. 4D may be called double-surface etching-type phase-shift photomask or double-surface etching-type substrate etching phase-shift photomask.
However, when the phase-shift photomask shown in FIG. 4D is used to obtain effect of correction by the isotropic etching, the side etching amounts Wb1 and Wb2 are made large and a projecting portion having a hood-like shape (hood-like portions, hereinlater) 325 formed to the light-blocking (light-shielding) material (film) 320 are made fragile in structure. The portions of the light-blocking material to which such hood-like portions 325 are formed to be liable to be peeled during a photomask washing process or like and hence become a cause of occurrence of a defective material or product, which will be called xe2x80x9cpeeled defectivexe2x80x9d hereinlater, and moreover, the sum of the Wb1 and Wb2 becomes large, so that the entire structure of the light-blocking films 320, whose both sides are subjected to the side etching process, becomes easily peelable.
In these days, the single-surface etching-type phase-shift photomask shown in FIG. 4C and the double-surface etching-type phase-shift photomask shown in FIG. 4D have been used as the etching-type phase-shift photomask as shown in FIG. 4B. However, the single-surface etching-type phase-shift photomask shown in FIG. 4C does not provide the structure for sufficiently solving the problem of the difference in dimension of the resists on the wafer corresponding respectively to the etched portion and non-etched portion. On the other hand, in the double-surface etching-type phase-shift photomask shown in FIG. 4D, the sum of Wb1 and Wb2 becomes large to obtain sufficient dimension correction effect, and the portions corresponding to the portions of Wb1 and Wb2 are liable to be peeled during a photomask washing process or like and hence become a cause of the xe2x80x9cpeeled defectivexe2x80x9d. Moreover, the entire structure of the light-blocking films 320 becomes easily peelable as mentioned above, thus also providing a problem.
An object of the present invention is to substantially eliminate defects or drawbacks encountered in the prior art mentioned above and to provide a method of manufacturing a phase-shift photomask, particularly of an etching-type phase-shift photomask manufacturing method, capable of solving the problem of the difference in dimension of resists on a wafer corresponding to etched portion and non-etched portion and also provide a phase-shift photomask manufactured by such method having a structure having strength suitable for a practical use.
This and other objects can be achieved according to the present invention by providing, in one aspect, a method of manufacturing a phase-shift photomask comprising the steps of:
preparing a substrate transparent to an exposure light having a wavelength xcex and having a refraction factor n;
forming, on the substrate, a pattern including light-blocking portion blocking the light entering and light transmission portion including a plurality of light transmission sections transmitting light; and
etching the substrate on the transmission portion so as to provide adjacent transmission sections with recesses one having a depth d1 and the other one having a depth d2 so as to satisfy an equation of (d1xe2x88x92d2)=xcex/2(nxe2x88x921),
the etching step comprising a first etching process of a dry-etching selective to the light transmission section of the substrate having the depth d1 so as to provide a predetermined depth D1 after the formation of the light-blocking portion, a second etching process of a wet-etching process selective to the transmission section having the depth d1 so as to provide a depth of xcex/2(nxe2x88x921), and a third etching process step of a wet-etching to all the light transmission sections having the depth d1 and the depth d2 so as to satisfy an equation of (d1xe2x88x92d2)=xcex/2(nxe2x88x921).
In preferred embodiments or examples in this method, the phase-shift photomask is a Levenson-type phase-shift photomask. The phase-shift photomask is a photomask for KrF eximer laser having an exposure light wavelength xcex of 248 nm. The phase-shift photomask is a photomask for ArF eximer laser having an exposure light wavelength xcex of 193 nm. The phase-shift photomask is a photomask for F2 eximer laser having an exposure light wavelength xcex of 157 nm.
An etching depth to the substrate in the third etching process is not less than 10 nm and not more than 50 nm.
Providing that xcex4 is [xcex2(nxe2x88x921)]/9, a length difference (d1xe2x88x92d2) between said depth d1 and said depth d2 is in a range from [xcex/2(nxe2x88x921)]+xcex4 to [xcex/2(nxe2x88x921)]xe2x88x92xcex4.
In another aspect of the present invention, there is also provided a phase-shift photomask comprising;
a substrate transparent to an exposure light having a wavelength xcex and having a refraction factor n; and
a pattern, formed on the substrate, including light-blocking portion blocking the light entering and light transmission portion transmitting light,
the light transmission portion including a plurality of light transmission sections in which one of adjacent light transmission sections is etched so as to provide a recess having a depth d1 and the other one of the adjacent light transmission sections is etched so as to provide a recess having a depth d2 so as to satisfy an equation of (d1xe2x88x92d2)=xcex/2(nxe2x88x921),
wherein portions of the recesses continuous to the light blocking portion are subjected to a wet-etching process with different side-etching amounts to thereby form hood-like portions having different lengths from each other.
In preferred embodiments or examples in this aspect, the phase-shift photomask may be made to various type ones as mentioned above.
Further, a difference, on the side of the light transparent sections, between a length of the hood-like portion of the recess having the depth d1 and a length of the hood-like portion of the recess having the depth d2 may be made to be not less than 0 and not more than 200 nm.
According to the present invention of the characters mentioned above, the problem in dimensions of the resists on the wafer corresponding to the etched portions and non-etched portions can be solved, and therefore, a phase-shift photomask having practical strength and etched structure can be provided.
That is, more in detail, with reference to FIG. 4, which will be explained hereinlater, according to the present invention, there can be solved the problem in dimensions of the resist images on a wafer corresponding to the etched portion and non-etched portion of a single-etching type phase-shift photomask (such as shown in FIG. 4C), and in a case where a sufficient dimension correction effects could be expected, the problem that both side portions of the double-etching type phase-shift photomask are largely side-etched and peeling or cracking is inevitably generated.
More in detail, such functions and effects can be achieved by providing the phase-shift photomask manufacturing method in which the etching step is characterized by comprising a first etching process of a selective dry-etching to the light transmission section of the substrate having the depth d1 so as to provide a predetermined depth D1 in depth of less than xcex/2(nxe2x88x921) after the formation of the light-blocking portion, a second etching process of a wet-etching process to the transmission section having the depth d1 so as to provide a depth of xcex/2(nxe2x88x921), and a third etching process of a wet-etching to all the light transmission sections having the depth d1 and the depth d2 so as to satisfy an equation of (d1xe2x88x92d2)=xcex/2(nxe2x88x921).
By effecting the first and second etching processes, the single-etching type phase-shift photomask as in FIG. 4C, representing a conventional structure, is obtained, and then, by effecting the third etching process, the problem in dimension difference of the resists on the wafer corresponding to the etched portion and non-etched portion occurring in the structure of FIG. 4C can be solved as well as reducing the amount of peeling and cracking to the hood-like portions without requiring an excessively large dimension (Wb) of Wb1 and Wb2 of the side-etching amount (i.e., length of the cantilevered portion) through the wet-etching process to the light transmission section (depth d1) of the light blocking film.
The Levenson type phase-shift photomask will be most effectively applied to a hole pattern oblique arrangement in size of less than 1.0 xcexcm.
Furthermore, the case of the phase-shift photomask for KrF eximer laser having an exposure light wavelength xcex of 248 nm is effective, the case of the phase-shift photomask for ArF eximer laser having an exposure light wavelength xcex of 193 nm is more effective, and the case of the phase-shift photomask for F2 eximer laser having an exposure light wavelength xcex of 157 nm is specifically effective.
Further, in order to make possible reductions in the side-etching amount in the wet-etching process in the second and third etching processes, it will be desired that the etching amount (depth) D1 in the first etching process is to be an amount causing approximately 50 to 70 degree phase-shift in view of the light intensity regulation (correction). In such case, it is necessary to provide an etching depth in the third etching process to be more than 10 nm in view of the light intensity regulation, but in consideration of the peeling of the light-blocking film, it will be preferred that the etching depth in the third etching process is less than 50 nm in the present invention.
Furthermore, this effect in view of the light intensity regulation will be more effective in the case providing that xcex4 is [xcex/2(nxe2x88x921)]/9, a length difference (d1xe2x88x92d2) between the depth d1 and the depth d2 is in a range from (2mxe2x88x921)xcex/2(nxe2x88x921)+xcex4 to (2mxe2x88x921)xcex/2(nxe2x88x921)xe2x88x92xcex4. In this equation, m stands for an integer of 1 or above. In this case, it is preferred to use m=1, the length difference (d1xe2x88x92d2) described above is in a range from xcex/2(nxe2x88x921)+xcex4 to xcex/2(nxe2x88x921)xe2x88x92xcex4.
The nature and further characteristic features of the present invention will be made more clear from the following descriptions made with reference to the accompanying drawings.